In making that determination, Mnuchin said he relied on the advice of the Justice Department. He concluded that the department is “not authorized to disclose the requested returns and return information.”

The move, which was expected, is sure to set in motion a legal battle over Trump’s tax returns. The chief options available to Democrats now are to subpoena the Internal Revenue Service for the returns or to file a lawsuit.

Neal originally demanded access to Trump’s tax returns in early April under a law that says the IRS “shall furnish” the returns of any taxpayer to a handful of top lawmakers, including the chair of the tax-writing Ways and Means Committee.

WATCH: Democrats provide April 23 deadline for Trump to release his tax returns

The White House and the president’s attorneys declined to comment on the deadline to turn over Trump’s returns.

Trump has privately made clear he has no intention of turning over the much-coveted records.

The president has told those close to him that the attempt to get his returns was an invasion of his privacy and a further example of what he calls the Democrat-led “witch hunt” — like special counsel Robert Mueller’s probe — meant to damage him.

Trump has repeatedly asked aides as to the status of the House request and has not signaled a willing to cooperate with Democrats, according to a White House official and two Republicans close to the White House.

He has linked the effort to the myriad House probes into his administration and has urged his team to stonewall all requests. He also has inquired about the “loyalty” of the top officials at the IRS, according to one of his advisers.

Trump has long told confidants that he was under audit and therefore could not release his taxes. But in recent weeks, he has added to the argument, telling advisers that the American people elected him once without seeing his taxes and would do so again, according to the three White House officials and Republicans, who were not authorized to speak publicly about private conversations.